JP2009136069A - High-voltage power supply device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-voltage power supply device using a piezoelectric transformer wherein failure in the output images of an image forming apparatus due to interference between driving frequencies in the piezoelectric transformer is suppressed and an image forming apparatus using this power supply device. <P>SOLUTION: The pattern of the high-voltage power supply device having multiple high-voltage power supply circuits is constructed as follows: a pattern of ground potential is run parallel to and wired adjacently to a wiring pattern between the secondary output terminals of the piezoelectric transformer and a rectifying circuit; and the adjacent parallel wiring distance is made different from drive circuit to drive circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high voltage power supply apparatus suitable for an image forming apparatus that forms an image by an electrophotographic process, and more particularly to a high voltage power supply apparatus using a piezoelectric transformer and an image forming apparatus having the high voltage power supply apparatus.

  In recent years, color laser printers and copiers form a color image by scanning a plurality of photoconductors with light beams independently from a plurality of optical devices, and superimposing the color images on an intermediate transfer belt. A tandem method is used in which a color image is formed by transferring to a sheet. Since the tandem method forms four color images at a time, the time required to form a final color image can be greatly shortened, which contributes to the realization of higher speed image forming apparatuses.

  A specific configuration and operation of the tandem color laser printer will be described with reference to FIG. Laser light from the laser scanner (11Y, 11M, 11C, 11K) is applied to the surface of the photoconductor (13Y, 13M, 13C, 13K) charged by the charging bias applied to the charging roller (15Y, 15M, 15C, 15K). An electrostatic latent image is formed by irradiation, and is visualized by attaching toner with a developing bias applied to a developing device (16Y, 16M, 16C, 16K). Subsequently, the toner adhering to the photoconductors (13Y, 13M, 13C, 13K) is sequentially superposed on the intermediate transfer belt 19 by the transfer bias applied to the transfer rollers (18Y, 18M, 18C, 18K). Transferred to form a full color toner image. On the other hand, the paper 21 in the cassette 22 is fed by the paper feed roller 25 at a timing coincident with the toner image on the intermediate transfer belt 19 by the secondary transfer roller 29. Then, it is conveyed by the registration roller 27, and the full-color toner image on the intermediate transfer belt 19 is transferred onto the paper 21 by the secondary transfer roller 29. Further, the paper 21 on which the full-color toner image is placed is fixed by the fixing device 30 to finally obtain a full-color printed matter.

  In the electrophotographic process operation described above, a DC bias voltage is used for the charging bias applied to the charging roller, the developing bias applied to the developing device, and the transfer bias applied to the transfer roller. Each bias required for the image forming process requires a high voltage. For example, a transfer bias usually requires a voltage of 3 kV or more for good transfer.

  Conventionally, a wound electromagnetic transformer has been used to generate a high voltage in an image forming apparatus. However, an electromagnetic transformer is composed of a copper wire, bobbin, and magnetic core. When a voltage of 3 kV or more is applied as described above, the output current value is several μA, so that each part has a small output current value. And leakage current had to be minimized. Therefore, it is necessary to mold the winding of the transformer with an insulator, and a transformer larger than the supplied power is required, which hinders the miniaturization and weight reduction of the high-voltage power supply device.

  In order to compensate for these problems, a high voltage generator that generates a high voltage using a thin, lightweight, high-power piezoelectric transformer has begun to be used. That is, by using a piezoelectric transformer made of a ceramic material, it is possible to generate a high voltage with an efficiency higher than that of an electromagnetic transformer. In addition, since the distance between the primary and secondary electrodes can be increased regardless of the coupling between the primary side and the secondary side, it is not necessary to perform special molding for insulation. Therefore, there is an advantage that the high-pressure generator can be reduced in size and weight, which contributes to downsizing of the apparatus.

  An example of a high-voltage power supply device using a piezoelectric transformer is disclosed in Patent Document 1.

  An example of a high-voltage power supply circuit using a piezoelectric transformer will be described with reference to FIG. The circuit example shown in FIG. 9 shows an example of a charging system circuit that outputs a negative bias as an example. In FIG. 9, 101Y is a piezoelectric transformer (piezoelectric ceramic transformer) of a high voltage power source. The output of the piezoelectric transformer 101Y is rectified and smoothed to a negative voltage by the diodes 102Y and 103Y and the high-voltage capacitor 104Y, and supplied from the output end 116Y to a charging roller (not shown) as a load. The output voltage is divided by the resistors 105Y, 106Y, and 107Y, and input to the non-inverting input terminal (+ terminal) of the operational amplifier 109Y through the protective resistor 108Y. On the other hand, a high-voltage power supply control signal (Vcont), which is an analog signal, is input to the connection terminal 118Y via a resistor 114Y from an inverting input terminal (-terminal) of the operational amplifier. By forming an integration circuit with the operational amplifier 109Y, the resistor 114Y, and the capacitor 113Y, a control signal (Vcont) smoothed with an integration time constant determined by the component constants of the resistor and the capacitor is input to the operational amplifier 109Y. The output terminal of the operational amplifier 109Y is connected to a voltage controlled oscillator (VCO) 110Y, and the output terminal is connected to a transistor 111Y connected to an LC parallel resonant circuit formed by an inductor 112Y and a capacitor 115Y. The voltage controlled oscillator (VCO) 110Y operates to lower the output frequency when the input voltage increases, and to increase the output frequency when the input voltage decreases. Therefore, the voltage controlled oscillator (VCO) 110Y changes to the input level. The corresponding frequency is output. The output signal of the voltage controlled oscillator (VCO) 110Y drives the LC resonance circuit, so that power corresponding to the control signal (Vcont) is finally supplied to the primary side of the piezoelectric transformer.

FIG. 10 is a diagram showing the characteristics of the output voltage with respect to the driving frequency of the piezoelectric transformer 110Y. As shown in the figure, the output voltage becomes maximum at the resonance frequency f0, and it can be seen that the output voltage can be controlled by the frequency. The drive frequency when the specified output voltage Edc is output is fx. The voltage controlled oscillator (VCO) 110Y has a drive frequency that changes according to the control signal (Vcont). When the output voltage Edc is controlled to obtain a higher voltage, the drive drive frequency is a frequency lower than fx. It will be driven by. Further, when the output voltage Edc is controlled by obtaining a lower voltage, the drive drive frequency is driven at a frequency higher than fx. In other words, the output voltage of the high-voltage drive circuit shown in FIG. 9 is controlled at a constant voltage so as to be equal to the voltage determined by the voltage of the control signal (Vcont) input to the inverting input terminal (−terminal) of the operational amplifier 109Y. The negative feedback control circuit is configured such that the output voltage is controlled at a constant voltage.
JP-A-11-206113

  The high voltage power supply circuit of the electrophotographic image forming apparatus has independent biases such as charging, developing, and transfer corresponding to the image forming portions of yellow (Y), magenta (M), cyan (C), and black (K). In this case, a plurality of piezoelectric transformers and control circuits shown in FIG. 9 are disposed on the high-voltage power supply substrate. In particular, in a tandem color image forming apparatus, each bias is driven simultaneously, and each circuit corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) is provided. Controlled to substantially the same bias output voltage. At this time, the piezoelectric transformer mounted on the high-voltage power supply unit is driven at substantially the same frequency (adjacent frequency) by four circuits for each charging, developing, and transfer bias.

  However, when a plurality of piezoelectric transformers are driven at close frequencies and the same bias voltage is output as described above, the piezoelectric transformers connected to the same power supply line cause mutual interference via the power supply line, and the interference frequency is reduced. Due to the influence, the output bias may fluctuate, which may cause image damage.

  FIG. 11 is a diagram showing frequency characteristics of a plurality of piezoelectric transformers. The resonance frequency f0 of the piezoelectric transformer is not the same due to variations in solids, and a slight difference occurs as shown in FIG. This difference is several tens Hz to several hundreds Hz. Therefore, in order for the two drive circuits to output the same voltage Edc, they are driven at the drive frequencies fx and fx ′, respectively. For example, when the two drive waveforms described in FIG. 11 are superimposed, the superimposed voltage is maximized at a period of fbeet = | fx−fx ′ | (Hz), and appears as a large beat as an intermodulation beat in the output waveform. For example, when the yellow (Y) drive circuit is driven at 200 KHz and the magenta (M) drive circuit is driven at 200.1 KHz, the cross-modulation beat ripple of 100 Hz, which is the difference between them, is the power source. It appears on the line, and finally the output voltage becomes a waveform that fluctuates at 100Hz.

  When this interference frequency fbeet appears in the high voltage output, for example, when it is a transfer bias, it appears as a periodic fluctuation in transfer efficiency, and when it is a charging / developing bias, a periodic fluctuation occurs in the image density. As a result, assuming that the process speed is PS (mm / s), the output image has an adverse effect such as an output image having a density difference with a period of Tb = PS / fbeet (mm) and being output as a striped interference image. End up.

  In recent years, as a countermeasure against making the drive frequencies different so as not to be close to each other, a capacitor for a resonance frequency varying means may be provided between the transformer output terminal and the rectifying means connected. However, a high voltage capacitor is required to connect to the secondary side of the transformer, leading to an increase in cost.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a power supply device using a piezoelectric transformer that suppresses interference between driving frequencies in the piezoelectric transformer and enables miniaturization and high image quality. To do.

  The above object is achieved by the image forming apparatus according to the present invention. In order to achieve the above object, according to the first aspect of the present invention, a plurality of high-voltage power supply circuits are provided on a printed circuit board, and each of the high-voltage power supply circuits corresponds to a piezoelectric transformer and a control signal. A high-voltage power supply device comprising a frequency-controlled oscillator that generates a signal of the piezoelectric transformer drive frequency and a drive circuit that receives the control signal and drives the piezoelectric transformer, wherein the secondary side of the piezoelectric transformer of at least one high-voltage power supply circuit A stray capacitance is created by placing a ground potential pattern close to the wiring pattern between the output terminal and the rectifier circuit. This stray capacitance makes the resonance frequency of the piezoelectric transformer different from the resonance frequency of other piezoelectric transformers. A piezoelectric transformer drive circuit pattern characterized by the above, and a high-voltage power supply apparatus having the pattern.

  Further, according to the second aspect of the present invention, the parallel running distance of the ground potential pattern arranged close to the wiring pattern between the piezoelectric transformer secondary output terminal of the one high-voltage power supply circuit and the rectifier circuit Is a length different from the parallel running distance of the ground potential pattern arranged close to the wiring pattern between the piezoelectric transformer secondary output terminal of the other high-voltage power supply circuit and the rectifier circuit. A transformer driving circuit pattern and a high-voltage power supply device having the pattern.

  According to the third aspect of the present invention, the wiring pattern between the piezoelectric transformer secondary output terminal and the rectifier circuit of the one high-voltage power supply circuit is arranged close to the ground potential pattern on one side, Piezoelectric transformer driving circuit pattern, characterized in that a ground potential pattern is arranged close to both sides of a wiring pattern between the piezoelectric transformer secondary output terminal and the rectifier circuit of another one high-voltage power supply circuit, and the pattern Is a high-voltage power supply device.

  According to the fourth aspect of the present invention, the wiring pattern between the piezoelectric transformer secondary output terminal of the one high-voltage power supply circuit and the rectifier circuit, and the ground potential pattern arranged in the vicinity of the output line Is different from the interval between the wiring pattern between the output terminal of the piezoelectric transformer secondary side of the other high-voltage power supply circuit and the rectifier circuit and the pattern of the ground potential wired close to the output line. A piezoelectric transformer drive circuit pattern and a high-voltage power supply device having the pattern.

  According to the fifth aspect of the present invention, there is provided a wiring pattern between the piezoelectric transformer secondary output terminal of the high-voltage power supply circuit and the rectifier circuit, and a ground potential pattern arranged close to the output line. A piezoelectric transformer driving circuit pattern characterized in that a slit is formed in between, and a high-voltage power supply apparatus having the pattern.

  According to the sixth aspect of the present invention, a plurality of high-voltage power supply circuits are provided on the printed circuit board, and each high-voltage power supply circuit outputs a piezoelectric transformer and a signal of the piezoelectric transformer drive frequency in accordance with a control signal. A high-voltage power supply device having a double-sided board configuration having a generated frequency-controlled oscillator and a drive circuit for driving a piezoelectric transformer in response to the control signal, and rectifying the secondary-side output terminal of the piezoelectric transformer of at least one high-voltage power supply circuit A piezoelectric transformer driving circuit pattern characterized in that the resonant frequency of a plurality of piezoelectric transformers is made different by arranging a ground potential pattern in parallel on the back side of the wiring pattern between circuits, and the pattern It is a high-voltage power supply device.

  According to the seventh aspect of the present invention, the parallel arrangement of ground potential patterns arranged in parallel on the back side of the wiring pattern between the piezoelectric transformer secondary output terminal of the one high-voltage power supply circuit and the rectifier circuit is provided. The running distance is different from the parallel running distance of the ground potential pattern wired in parallel on the back side of the wiring pattern between the piezoelectric transformer secondary output terminal of the other high-voltage power supply circuit and the rectifier circuit. A characteristic piezoelectric transformer drive circuit pattern and a high-voltage power supply device having the pattern.

  According to an eighth aspect of the present invention, there is provided an image forming apparatus comprising the high-voltage power supply device according to any one of the first to seventh aspects.

  According to the first aspect of the present invention, a ground potential pattern is arranged close to the piezoelectric transformer secondary output line of at least one high-voltage power supply circuit, so that the piezoelectric transformer output line and the ground pattern are disposed between each other. A stray capacitance is formed. As a result, the resonance frequency of the piezoelectric transformer changes, and it becomes possible to reduce intermodulation beat ripple due to frequency interference with a high-voltage power supply circuit in which other ground potential patterns are not arranged close to each other.

  According to the second aspect of the present invention, the parallel running distance between the secondary output line of the piezoelectric transformer and the ground potential pattern is set to a different length for each of the plurality of drive circuits. Stray capacitances of different sizes are formed on the secondary side. As a result, the resonance frequencies of the plurality of drive circuits can be shifted, and the intermodulation beat ripple due to frequency interference can be reduced.

  According to the third aspect of the present invention, the ground potential patterns are arranged close to one side only by arranging the ground potential patterns close to both sides of the piezoelectric transformer secondary output line. A stray capacitance having a size different from that of the piezoelectric transformer driving circuit is formed. As a result, the resonance frequencies of the plurality of drive circuits can be shifted, and the intermodulation beat ripple due to frequency interference can be reduced.

  According to the fourth aspect of the present invention, the distance between the patterns arranged close to the piezoelectric transformer output line and the ground line is set to be different for each drive circuit. Stray capacitances of different sizes are formed on the next side. As a result, the resonance frequencies of the plurality of drive circuits can be shifted, and the intermodulation beat ripple due to frequency interference can be reduced.

  Further, according to the fifth aspect of the present invention, by providing a slit between the piezoelectric transformer output line and the ground line arranged close to the piezoelectric transformer output line, a sufficient creepage distance between the high-voltage line and the low-voltage line is provided on the printed circuit board. It is possible to secure and form a stray capacitance.

  According to the sixth aspect of the present invention, the stray capacitance is generated between the piezoelectric transformer output line and the ground pattern by running the ground pattern in parallel on the back side of the piezoelectric transformer secondary output line on the double-sided board. It is formed. As a result, the resonance frequency of the piezoelectric transformer changes, and it becomes possible to reduce cross-modulation beat ripple due to frequency interference with a high-voltage power supply circuit in which a ground potential pattern is not arranged in parallel on the other back surface.

  According to the seventh aspect of the present invention, the parallel running distances of the ground patterns that run parallel to the back side of the secondary output line of the piezoelectric transformer with respect to the plurality of drive circuits in the double-sided board are different. As a result, the resonance frequencies of the plurality of drive circuits can be shifted, and the intermodulation beat ripple due to frequency interference can be reduced.

  According to an eighth aspect of the present invention, there is provided an image forming apparatus equipped with a high voltage power supply device using a piezoelectric transformer in which frequency interference between the high voltage power supply circuits is reduced or prevented. It makes it possible to obtain a good and stable image.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. However, this embodiment is merely an example, and the present invention is not limited to these configurations.

  FIG. 1 is a configuration diagram of a tandem color image forming apparatus using an electrophotographic process.

  The image forming operation of the configuration of the image forming apparatus will be described with reference to FIG. The tandem color image forming apparatus is configured to output a full color image by superimposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K). Laser scanners (11Y, 11M, 11C, 11K) and cartridges (12Y, 12M, 12C, 12K) are provided for image formation of each color. The cartridge (12Y, 12M, 12C, 12K) includes a photoconductor (13Y, 13M, 13C, 13K) that rotates in the direction of the arrow in the figure, and a photoconductor cleaner (14Y, 14M, 14K) provided in contact with the photoconductor. 14C, 14K), a charging roller (15Y, 15M, 15C, 15K), and a developing unit having a developing roller (16Y, 16M, 16C, 16K) and a blade (17Y, 17M, 17C, 17K). . Further, an intermediate transfer belt 19 is provided in contact with each color photoconductor (13Y, 13M, 13C, 13K), and a primary transfer roller (18Y, 18M, 18C, 18K) is provided so as to sandwich the intermediate transfer belt 19 and face each other. Is installed. Further, the intermediate transfer belt 19 is provided with a belt cleaner 20 and a waste toner container 31 in which scraped waste toner is stored. The cassette 22 that stores the paper 21 is provided with a size guide 23 that regulates the position of the paper 21 in the cassette 22 and a paper presence sensor 24 that detects the presence or absence of the paper 21 in the cassette 22. A paper feed roller 25, separation rollers 26a and 26b, and a registration roller 27 are provided in the conveyance path of the paper 21, and a registration sensor 28 is provided in the vicinity of the registration roller 27 on the downstream side in the paper conveyance direction. A secondary transfer roller 29 is in contact with the intermediate transfer belt 19, and a fixing device 30 is installed downstream of the secondary transfer roller 29.

  Reference numeral 40 denotes a controller which is a control unit of the laser printer, and includes a RAM 41a, a ROM 41b, an MPU (microcomputer) 41 having a timer 41c, and various input / output control circuits (not shown).

  Reference numeral 42 denotes a high-voltage power supply unit, which is a charging high-voltage power supply (not shown) corresponding to each process cartridge, a development high-voltage power supply (not shown), and a transfer high-voltage power supply (not shown) capable of outputting a high voltage corresponding to each transfer roller. The output is controlled by the controller 40 described above.

  Next, the electrophotographic process will be described. In the dark place in the cartridge (12Y, 12M, 12C, 12K), the surface of the photoreceptor (13Y, 13M, 13C, 13K) is uniformly charged by the charging roller (15Y, 15M, 15C, 15K). Next, the surface of the photosensitive member (13Y, 13M, 13C, 13K) is irradiated with laser light modulated in accordance with image data by the laser scanner (11Y, 11M, 11C, 11K), and the charged charges of the portion irradiated with the laser light are irradiated. Is removed to form an electrostatic latent image on the surface of the photoconductor (13Y, 13M, 13C, 13K). In the developing unit, toner is transferred from the developing roller (16Y, 16M, 16C, 16K) holding a constant amount of toner layer by the action of the blade (17Y, 17M, 17C, 17K) by the developing bias by the developing bias. By attaching the toner image to the image, a toner image of each color is formed on the surface of the photoreceptor (13Y, 13M, 13C, 13K).

  The toner image formed on the surface of the photoreceptor is attracted to the intermediate transfer belt 19 by a transfer bias at the nip portion between the photoreceptor and the intermediate transfer belt 19. Further, the image formation timing in each cartridge (12Y, 12M, 12C, 12K) is controlled by the timing according to the belt conveyance speed, and the respective toner images are sequentially transferred onto the intermediate transfer belt 19, so that finally the intermediate A full-color image is formed on the transfer belt.

  On the other hand, the paper 21 in the cassette 22 is transported by the paper feed roller 25, and only one paper 21 passes through the registration roller 27 and is transported to the secondary transfer roller 29 by the separation rollers 26 a and 26 b. The toner image on the intermediate transfer belt 19 is transferred to the sheet 21 at the nip portion between the secondary transfer roller 29 and the intermediate transfer belt 19 downstream of the registration roller. Finally, the toner image on the sheet 21 is heated and fixed by the fixing device 30. Processed and discharged out of the image forming apparatus.

  Next, the configuration of the piezoelectric transformer high-voltage power supply device 42 of this embodiment will be described with reference to FIG. Here, a description will be given of a charged high-voltage power supply as a representative. However, the high-voltage power supply configuration according to the present invention is effective for both positive voltage and negative voltage output circuits. The charging high-voltage power supply is provided with four circuits corresponding to the charging rollers 15Y, 15M, 15C, and 15K. Since the basic configurations of the Y, M, C, and K circuits are the same, Y will be described as a representative here.

  The output of the piezoelectric transformer 101Y is rectified and smoothed to a negative voltage by the diodes 102Y and 103Y and the high-voltage capacitor 104Y, and supplied from the output end 116Y to a charging roller (not shown) as a load. The output voltage is divided by the resistors 105Y, 106Y, and 107Y, and input to the non-inverting input terminal (+ terminal) of the operational amplifier 109Y through the protective resistor 108Y. On the other hand, a high-voltage power supply control signal (Vcont), which is an analog signal, is input to the connection terminal 118Y via a resistor 114Y from an inverting input terminal (-terminal) of the operational amplifier. By forming an integration circuit with the operational amplifier 109Y, the resistor 114Y, and the capacitor 113Y, a control signal (Vcont) smoothed with an integration time constant determined by the component constants of the resistor and the capacitor is input to the operational amplifier 109Y. The output terminal of the operational amplifier 109Y is connected to a voltage controlled oscillator (VCO) 110Y, and the output terminal is connected to a transistor 111Y connected to an LC parallel resonant circuit formed by an inductor 112Y and a capacitor 115Y. The voltage controlled oscillator (VCO) 110Y operates to lower the output frequency when the input voltage increases, and to increase the output frequency when the input voltage decreases. Therefore, the voltage controlled oscillator (VCO) 110Y changes to the input level. The corresponding frequency is output.

  FIG. 3 is an operation waveform of each part shown in FIG. Here, (1) is a voltage applied to the gate terminal of the FET 111Y, (2) is a voltage appearing at the drain terminal of the FET 111Y, (3) is a current flowing through the inductor 112Y, and (4) is a ripple voltage formed in the power supply line. Respectively.

  When the FET 111Y is turned on, a current flows through the inductor and the energy of the inductor is accumulated. Next, when the FET is turned off, resonance occurs between the inductor 112Y and the capacitor 115Y as shown in (2). Here, it is desirable that the capacitor 115Y is sufficiently larger than the equivalent capacitance existing on the primary side of the piezoelectric transformer, and it is desirable to select a constant that can ignore the primary side capacitance error due to variations in the body of the piezoelectric transformer. Further, when the resonance voltage is 0V, the resonance is efficiently and continuously repeated by driving so that the ON period of the FET starts.

  On the other hand, the power supply current flowing through the inductor 112Y during the resonance operation is represented by (3). When the FET 111Y is turned on, the current flows through the inductor 112Y and flows into the FET. Subsequently, even after the FET is turned off, current continues to flow so as to charge the capacitor 115Y by the inductive action of the inductor. Furthermore, after the current flowing through the inductor 112Y is 0 and the voltage appearing at the drain terminal of the FET 111Y is maximized, the current regenerative operation starts, and the current is supplied to the power supply side from the capacitor and the parasitic diode (not shown) inside the FET. It becomes a regenerative period that flows into. When the resonant operation of the inductor, the capacitor, and the FET is performed, when viewed from the power supply side, discharging (period <A> in the figure) and charging (period <B> in the figure) are repeated, and the power supply voltage is increased. As shown in (4), a constant ripple waveform corresponding to the drive cycle appears.

FIG. 4 is a schematic diagram of pattern wiring on a printed circuit board showing the features of this embodiment. For the purpose of explanation of this patent, this figure shows from the piezoelectric transformer (101Y, 101M, 101C, 101K) to the output end (106Y, 106M, 106C, 106K). This corresponds to the same numbered parts described in FIG. In the figure, line 200 is a ground potential pattern.
The characteristic point of this figure is that the wiring pattern between the piezoelectric transformer 101M and the rectifier diode 103M and the ground potential pattern are in close proximity and parallel to each other at the location indicated by <A>. In this embodiment, the parallel running distance L1 at the location <A> is 3 mm. On the other hand, the wiring pattern between the piezoelectric transformer 101C and the rectifier diode 103C and the ground potential pattern are running close to each other at the location indicated by <B>. In this embodiment, the parallel running distance L2 at the location <B> is 6 mm. Further, the wiring pattern between the piezoelectric transformer 101K and the rectifier diode 103K and the ground potential pattern are in close proximity and parallel to each other at a location indicated by <C>. In this embodiment, the parallel running distance L3 at the location <C> is 9 mm. However, each parallel running portion is provided with a slit having a certain width in order to ensure a creepage distance.

  In each of the locations <A>, <B>, and <C>, stray capacitance is formed between the output pattern on the secondary side of the piezoelectric transformer and the ground potential pattern, and the location of <A> is about 3 pF and <B>. A capacitance of approximately 6 pF is formed in the pattern and a capacitance of approximately 9 pF is formed in the pattern at the location of <C>.

  FIG. 5 is a diagram for explaining the frequency characteristics of the piezoelectric transformer in the case of the pattern configuration shown in FIG. In FIG. 5, 302 is a characteristic curve of the piezoelectric transformer 101M having a 3 pF stray capacitance, 303 is a characteristic curve of the piezoelectric transformer 101C having a 6 pF stray capacitance, and 304 is a 9 pF stray capacitance. 6 is a characteristic curve of the piezoelectric transformer 101K. As the stray capacitance present at the output terminal of the piezoelectric transformer increases, the maximum output frequency moves to the low frequency side. This is equivalent to increasing the internal capacitance existing on the secondary side of the piezoelectric transformer, and is a result of utilizing the change in the resonance frequency of the piezoelectric transformer.

  By increasing the difference between the drive frequencies in the above configuration, the ripple frequency of the intermodulation beat that appears at the output end of the piezoelectric transformer increases. However, the amplitude of the interference ripple at the output end of the piezoelectric transformer does not change. On the other hand, in the high voltage power supply circuit described with reference to FIG. 2, there is a low pass filter formed by the resistance of the capacitor 104Y and a load roller (not shown) connected to the output end. Due to the presence of this filter, the ripple amplitude of the voltage appearing at the output end 116Y appears when the load is connected. When the ripple frequency is increased in the above-described operation, an effect is obtained that the pitch interval of the density fluctuation becomes narrow in the output image, and the density fluctuation becomes difficult to be seen by human eyes. Further, since the ripple amplitude is further reduced, the density fluctuation appearing in the output image is reduced.

  As described above, according to the present embodiment, the parallel running distance in which the pattern of the ground potential is arranged in close parallel wiring to the wiring pattern between the piezoelectric transformer secondary output terminal of the high voltage power supply circuit and the rectifier circuit, and the other high voltage Printed high voltage power supply circuit with different lengths of parallel running distance of ground potential pattern on the secondary output line of power supply circuit and different stray capacitances on each secondary side of piezoelectric transformer Configure on the substrate. As a result, the drive frequency of each drive circuit can be greatly shifted, and the effect of shortening the period of the interference ripple appearing in the output voltage and reducing the amplitude can be obtained. As a result, it is possible to prevent image detrimental effects such as output of a striped interference image as the image forming apparatus.

  In the present embodiment, the parallel running pattern shown in the explanatory diagram is drawn linearly, but it is easily conceivable to secure a long parallel running distance with a small area by running in a curved and wavy shape. .

  Moreover, it is not always necessary to run in parallel, and only the GND pattern is wavy in a curved line, and the stray capacitance of each drive circuit unit may be changed by adopting a configuration in which it is close at several places.

  Furthermore, the pattern configuration example shown in the explanatory diagram is drawn on a single-sided substrate, and in the case of a double-sided substrate, a ground potential line 200 may exist on the back side with the substrate thickness interposed therebetween.

  Hereinafter, a second embodiment of the present invention will be described with reference to FIG.

  In the figure, 101Y, 101M, 101C, and 101K are piezoelectric transformers as in the first embodiment, and the line 200 is a ground potential pattern.

  This embodiment is different from the first embodiment in that ground lines are run in parallel on both sides of the output line of the piezoelectric transformer 101C and the output line of 101K. In this embodiment, the parallel running distance L4 shown in the figure is 3 mm, and L5 is 4 mm. As in the first embodiment, a stray capacitance of approximately 3 pF is formed at the output end of 101M, whereas a stray capacitance of approximately 6 pF is equivalently formed at the output end of 101C. Similarly, a stray capacitance of about 8 pF is formed at the output end of 101K, and the resonance frequency of each piezoelectric transformer is greatly shifted.

  The frequency characteristic curve due to the shift of the resonance frequency is the same as that described in the first embodiment, and the maximum output frequency moves to the low frequency side when the stray capacitance formed in the piezoelectric transformer output line is large. .

  According to this configuration, a larger capacitance can be secured by providing ground potential lines on both sides, which leads to a reduction in the substrate area from the piezoelectric transformer to the output end as compared with the configuration of FIG. 4 described in the first embodiment.

  In FIG. 6, for example, the ground potential line wired on both sides of the piezoelectric transformer 101C is drawn from the transformer primary side terminal, but this can also use the ground potential line of the adjacent 101M. .

  As described above, according to the present embodiment, a circuit in which a ground potential pattern is arranged in parallel and adjacent to the wiring pattern between the secondary output terminal of the piezoelectric transformer of the high-voltage power supply circuit and the rectifier circuit, and the other piezoelectric transformer 2 The wiring pattern between the output terminal on the secondary side and the rectifier circuit is different in the parallel running distance of the circuit in which the ground potential pattern is arranged in parallel on both sides, and there is a different stray capacitance on the secondary side of each piezoelectric transformer. A high-voltage power supply circuit is constructed on the printed circuit board. As a result, the drive frequency of each drive circuit can be greatly shifted, and the effect of shortening the period of the interference ripple appearing in the output voltage and reducing the amplitude can be obtained. As a result, it is possible to prevent image detrimental effects such as output of a striped interference image as the image forming apparatus.

  Hereinafter, a third embodiment of the present invention will be described with reference to FIG.

  In the figure, 101Y, 101M, 101C, and 101K are piezoelectric transformers as in the first embodiment, and the line 200 is a ground potential pattern.

  A pattern of ground potential with a parallel running distance L6 = 3 mm runs in parallel with the output line of the piezoelectric transformer 101M with an interval of L7 = 2 mm. On the other hand, a ground potential pattern with a parallel running distance L6 = 3 mm is running in parallel with the output line of the piezoelectric transformer 101M with an interval of L8 = 1 mm. The stray capacitance formed differs depending on the difference in distance from the ground potential. Specifically, a stray capacitance of about 1.5 pF is formed at the output end of 101M, whereas a stray capacitance of about 3 pF is equivalently formed at the output end of 101C. Similarly to the second embodiment, ground potential patterns run in parallel at the output end of 101K, and a stray capacitance of about 6 pF is formed. With this configuration, the resonance frequency of each piezoelectric transformer is greatly shifted.

  According to this configuration, the gap between the output line of the piezoelectric transformer and the ground potential is different, so that the stray capacitance formed in the output line of each piezoelectric transformer has a difference in size. This increases the degree of freedom of the pattern by combining with the configurations of the first and second embodiments, leading to a reduction in the substrate area from the piezoelectric transformer to the output end.

  As described above, according to the present embodiment, a circuit in which a ground potential pattern is adjacently connected in parallel at a first interval to a wiring pattern between a piezoelectric transformer secondary output terminal of a high-voltage power supply circuit and a rectifier circuit. Each of the piezoelectric transformers by providing a wiring pattern between the secondary output terminal of the other piezoelectric transformer and the rectifier circuit and a circuit in which a ground potential pattern is arranged in parallel and parallel at an interval different from the first interval. A high-voltage power supply circuit having different stray capacitances on the secondary side is formed on the printed circuit board. As a result, the drive frequency of each drive circuit can be greatly shifted, and the effect of shortening the period of the interference ripple appearing in the output voltage and reducing the amplitude can be obtained. As a result, it is possible to prevent image detrimental effects such as output of a striped interference image as the image forming apparatus.

1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. High-voltage power supply circuit diagram illustrating an embodiment of the present invention Voltage-current waveform diagram for explaining the circuit operation of the embodiment of the present invention Schematic diagram of pattern wiring on a printed circuit board, explaining Example 1 of the present invention FIG. 3 is a frequency characteristic diagram of a piezoelectric transformer illustrating Example 1 of the present invention. Schematic diagram of pattern wiring on a printed circuit board, explaining Example 2 of the present invention Schematic diagram of pattern wiring on a printed circuit board, explaining Example 3 of the present invention 1 is a schematic sectional view of an image forming apparatus according to a conventional example of the present invention. High voltage power supply circuit diagram illustrating a conventional example of the present invention Frequency characteristic diagram of piezoelectric transformer in conventional example of the present invention Frequency characteristic diagram of a plurality of piezoelectric transformers in the conventional example of the present invention

Explanation of symbols

12Y, 12M, 12C, 12K Cartridge 13Y, 13M, 13C, 13K Photoconductor 15Y, 15M, 15C, 15K Charging roller 16Y, 16M, 16C, 16K Developing roller 18Y, 18M, 18C, 18K Transfer roller 42 High voltage power supply 101 Piezoelectric transformer

Claims (8)

A plurality of high-voltage power supply circuits are provided on a printed circuit board, and each high-voltage power supply circuit includes a piezoelectric transformer, a frequency controlled oscillator that generates a signal of the piezoelectric transformer driving frequency in response to a control signal, and a piezoelectric transformer that receives the control signal A high-voltage power supply device having a drive circuit for driving
A stray capacitance is created by placing a ground potential pattern in close proximity to the wiring pattern between the output terminal of the piezoelectric transformer secondary side of the at least one high-voltage power supply circuit and the rectifier circuit, and the resonance frequency of the piezoelectric transformer is caused by this stray capacitance. A high-voltage power supply device characterized by being different from the resonance frequency of other piezoelectric transformers.   The parallel running distance of the ground potential pattern arranged close to the wiring pattern between the piezoelectric transformer secondary output terminal and the rectifier circuit of the one high-voltage power supply circuit is the output of the piezoelectric transformer secondary side of the other high-voltage power supply circuit. 2. The high-voltage power supply device according to claim 1, wherein the length is different from a parallel running distance of a ground potential pattern arranged in proximity to the wiring pattern between the terminal and the rectifier circuit.   The wiring pattern between the piezoelectric transformer secondary output terminal of one high-voltage power supply circuit and the rectifier circuit is arranged close to the ground potential pattern on one side, and the piezoelectric transformer secondary output of the other high-voltage power supply circuit. 2. The high-voltage power supply device according to claim 1, wherein a ground potential pattern is arranged close to both sides of the wiring pattern between the terminal and the rectifier circuit.   The interval between the wiring pattern between the piezoelectric transformer secondary output terminal of one high-voltage power supply circuit and the rectifier circuit and the ground potential pattern arranged in the vicinity of the output line is the secondary of the piezoelectric transformer of the other high-voltage power supply circuit. 2. The high-voltage power supply device according to claim 1, wherein the gap is different from a gap between a wiring pattern between the side output terminal and the rectifier circuit and a ground potential pattern wired close to the output line.   A slit is formed between a wiring pattern between the piezoelectric transformer secondary output terminal of the high-voltage power supply circuit and the rectifier circuit, and a ground potential pattern disposed in the vicinity of the output line. The high-voltage power supply device according to any one of claims 1 to 4. A plurality of high-voltage power supply circuits are provided on a printed circuit board, and each high-voltage power supply circuit includes a piezoelectric transformer, a frequency controlled oscillator that generates a signal of the piezoelectric transformer driving frequency in response to a control signal, and a piezoelectric transformer that receives the control signal A high-voltage power supply device having a double-sided board structure having a drive circuit for driving
The resonance frequency of the plurality of piezoelectric transformers is made different by arranging the ground potential pattern in parallel on the back side of the wiring pattern between the secondary transformer output terminal of the at least one high-voltage power supply circuit and the rectifier circuit. High-voltage power supply device characterized by   The parallel running distance of the ground potential pattern wired in parallel on the back side of the wiring pattern between the piezoelectric transformer secondary output terminal and the rectifier circuit of the one high-voltage power supply circuit is the piezoelectric transformer secondary of the other high-voltage power supply circuit. 7. The high-voltage power supply device according to claim 6, wherein the length is different from the parallel distance of the ground potential pattern wired in parallel on the back side of the wiring pattern between the side output terminal and the rectifier circuit.   An image forming apparatus comprising the high-voltage power supply device according to claim 1.

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